The present invention relates to method of and apparatus for forming metallic articles by cold extrusion, and, more particularly, to cold extrusion method and apparatus suitable for consecutively producing annular metallic articles from annular metallic blanks.
There are two types of extrusion-forging methods which have been used conventionally for producing substantially annular metallic articles such as bushings, gears and so forth by plastic work from annular blanks having central holes therein.
In, for example, U.S. Pat. No. 4,038,860, a metallic blank, which has been suitably sized and shaped, is forced by a punch into a cavity formed between a die and a mandrel and a plastic flow of the blank material is caused thereby filling the cavity. Then, the punch and the mandrel are withdrawn and an article thus formed or molded is pushed out of the die to the same side as the the punch by knock-out pins. Thus, in this known method, the shaped product can be taken out only by being knocked out towards the blank inlet side. This means that this method cannot be applied in a case where the outside diameter of the product is greater than that of the blank. In addition, this method is not able to provide sufficiently high precision in the formation of the shaped product. Furthermore, the fact that the product is unable to possess greater diameter than the blank means that products of different sizes require blanks of corresponding sizes. In other words, it is not possible to make common use of blanks of the same size for products of different sizes. It is often experienced that a portion of a blank remains outside the die when the blank is pressed into the die cavity. Such a portion has to be removed after the cold working by taking an additional step resulting in disadvantages such as raised production cost, small yield and low productivity.
In, for example, U.S. Pat. No. 3,837,205, another method is proposed wherein blanks, each having a central bore, are discontinuously forced into a container and extruded in the direction of application of pressure to the blanks. In this known art, a mandrel also plays the role of an extruding punch; namely, for placing a new blank into the die cavity, the mandrel is temporarily withdrawn from a blank being cold-worked and is again inserted into the latter blank just before the commencement of pressing of the new blank.
This method also suffers from drawbacks due to the requirement for repetitional insertion and withdrawal of the mandrel. Namely, this method cannot be applied to a case where the inside diameter of the blank under the cold working is gradually increased or the case where the final product has a greater outside diameter than the blank. In addition, the shape of the mandrel is restricted inconveniently. Furthermore, in this known art, the product has to be knocked out of the blank inlet of the die, with resultant disadvantageous wear of the die and slight distortion of the product. This method, therefore, is not preferred from the view point of precision of the product. Furthermore, productivity is low and production costs high due to the difficulty encountered when taking out the product from the die and due to the necessity for a die having a complicated structure.
Accordingly, an object of the invention is to provide a cold extrusion method which makes it possible to produce, by a cold extrusion from an annular blank, an accurately molded annular article having an outside diameter smaller or greater than that of the annular blank.
Another object of the invention is to provide a cold extrusion method in which a steady extrusion is effected over the entire part of the material under extrusion by the generation of a back pressure in the die, thereby ensuring high precision both in size and shape.
Still another object of the invention is to provide a cold extrusion method in which the material is deformed beyond the limit of the free elongation thereof due to a three-dimensional compression effected with the assistance of the back pressure.
A further object of the invention is to provide a cold extrusion apparatus constructed to achieve high productivity.
According to one feature of the invention, a method of plastically working metallic articles is provided which comprises the steps of: forcibly inserting a hollow metallic blank, at a normal temperature, into a die cavity formed between a mandrel placed on a fixed base and a die concentrically surrounding the mandrel so that the blank is plastically deformed between the mandrel and the die; forcibly inserting a subsequent hollow metallic blank into the die cavity while the relative position between the mandrel, the die and the first said blank being plastically deformed therebetween is maintained unchanged; and urging the subsequent blank against the first-said blank being deformed to extrude the first-said blank forwardly out of the die whereby the first-said blank is formed into a tubular article.
According to another feature of the invention, an apparatus for plastically working metallic articles is provided which comprises: a container for constraining the outside diameter of a metallic blank; a die connected to the lower end of the container and adapted to determine the outside diameter of an article to be obtained; a mandrel placed on a fixed base and disposed in the container and the die substantially concentrically therewith to cooperate therewith to define a die cavity, the mandrel being adapted to constrain the inner diameter of the blank; a punch fixed to a slider and movable therewith to force the blank into the die cavity so that a preceding blank in the die cavity is extruded downwardly therefrom; the die, the mandrel and the container being momentarily united together by a blank in the die cavity to form a momentary unit; and means for lifting the momentary unit following up an upward movement of the slider and thus the punch.
These and other objects, features and advantages of the invention will become clear from the following description with reference to the accompanying drawings.